1. Field of the Invention
This invention relates to a fuel injection control device of an internal combustion engine to be used for automotive vehicles, etc. More particularly, it is concerned with a faillure-time control device for such fuel injection control device of the internal combustion engine, which is capable of performing the continuous operation of the engine, even when a sensor for detecting a quantity of intake air flow is out of order.
2. Discussion of Background
FIG. 7 of the accompanying drawing illustrates a conventional fuel injection control device of the internal combustion engine of the above-described type as disclosed, for example, in Unexamined Japanese Patent Publication No. 57623/1983. In the drawing, a reference numeral 1 designates an air inlet port; a numeral 2 refers to an air cleaner for cleaning the intake air as introduced from the air inlet port 1; a numeral 3 refers to an air flow-meter for measuring a quantity of the intake air which has passed through this air cleaner 2; a reference numeral 4 denotes a throttle chamber which forms a passageway for the intake air which has passed through the air flow-meter 3; a reference numeral 5 indicates a throttle valve provided in this throttle chamber 4 and for adjusting the intake air flow which passes through the throttle chamber; a numeral 6 refers to a by-pass passage which forms a deflecting passage between the up-stream part and the down-stream part of this throttle valve 5; a reference numeral 7 designates a flow control valve which is provided on the half-way in this by-pass passage 6 and adjusts the quantity of air flowing in and through the by-pass passage 6; a reference numeral 8 represents a by-pass port which forms a deflecting passage between the up-stream part and the down-stream part of the throttle valve 5 in the same manner as in the by-pass passage 6; a numeral 9 refers to an idle adjust screw for controlling the quantity of the intake air flowing in this by-pass port 8; a numeral 10 refers to an intake manifold which is formed integrally with the above-mentioned throttle chamber 4 and constitutes a passageway for the intake air which has passed through the throttle valve 5; a reference numeral 11 indicates a fuel injector provided at the terminal part of this intake manifold 10 and for jetting out the fuel into an internal combustion engine; and a reference numeral 12 designates the internal combustion engine to burn an air-fuel mixture introduced into it, which is composed of the intake air from the intake manifold 10 and the fuel supplied from the fuel injector 11. The internal combustion engine is constructed with a cylinder 12b, a piston 12a and a combustion chamber 12c defined by the cylinder and the piston. A reference numeral 13 designates a variable resistor for detecting an aperture (or a degree of opening) of the throttle valve 5; a numeral 14 refers to a water temperature sensor for detecting temperature of cooling water for the internal combustion engine; 15 refers to an engine speed sensor for detecting the number of revolutions of the internal combustion engine 12; a reference numeral 16 denotes a neutral switch for detecting a power transmission 17 to be at its neutral position; a numeral 18 refers to a vehicle speed switch for detecting speed of the vehicle to be at a predetermined value (for example, 10 km/h) or lower; a reference numeral 19 denotes a micro-computer which carrries out the arithmetic operations on the basis of input signals from the variable resistor 13 and water temperature sensor 14 through respective A/D converters 20 and 21 as well as input signals from the neutral switch 16 and the vehicle speed switch 18, to thereby produce an output to the flow control valve 7 through a D/A converter 22 and an output to the above-mentioned fuel injector 11. This micro-computer is constructed with an interface 19a for the input/output signals, a memory 19b storing therein command programs, and a micro-processor 19c to perform various arithmetic operations in accordance with these command programs.
In the following, explanations will be given as to the basic operations of the conventional fuel injection control device of the internal combustion engine as constructed in the above-mentioned manner. First of all, the intake air as introduced from the air inlet port 1 passes through the air cleaner 2 and the throttle chamber 4 to reach the intake manifold 10. On the other hand, the intake air is detected its quantity at the air flow-meter 3, the detected signal of which is processed in the micro-computer 19 to find out a fuel flow quantity commensurate with the intake air flow. On the basis of this fuel flow as calculated, the fuel injector 11 is driven and the fuel is thus jetted out for supply into the combustion chamber 12c in mixture with the intake air, where the fuel-air mixture is burned.
In the next place, explanations will be made as to the operations of the conventional fuel injection control device during idle running of the engine. First of all, the variable resistor 13 detects the approximately full closure state of the throttle valve 5, while the neutral switch 16 detects the neutral position occupied by the power transmission 17. Further, the vehicle speed switch 18 detects that the vehicle is at its speed lower than a predetermined value. These detection signals are all inputted into the micro-computer 19, and, as soon as all of the detection signals are obtained, the idling control is effected by the micro-computer 19. In more detail, the flow control valve 7 is actuated in such a manner that the number of revolution of the internal combustion engine 12 as detected by the engine speed sensor 15 may become equal to a set idling speed of the engine (e.g., 700 rpm) which has been stored in the memory 19b in advance, whereby the fuel injection control device is so operated as to adjust the air flowing in and through the by-pass passageway 6, and suppress waste in the fuel consumption at the time of the idle running of the engine.
The conventional fuel injection control device of the internal combustion engine attempts to improve operativeness of the engine as well as composition of the exhaust gas during the idle running by controlling the flow control valve 7 provided in the by-pass passageway 6 which circumvents the throttle valve 5. This conventional device, however, does not give any consideration whatsoever as to the point of enabling it to operate continuously even in the case of the air flow-meter 3 getting out of order.
On the other hand, the operation and the control of the fuel injection control device, when the sensor for detecting the intake air flow is out of order, have been known from, for example, Unexamined Japanese Patent Publication No. 148925/1980, the construction of which is as shown in FIG. 8.
In FIG. 8, a reference numeral 3 designates an intake air flow measuring device of a hot-wire type, for example, which measures the quantity of air flowing in and through the air intake passage; a numeral 23 refers to a mal-function detecting device which detects an abnormal operation in the intake air flow measuring device 3; a numeral 24 refers to a trouble indicator which indicates the disorder occurred in the intake air flow measuring device 3 on the basis of an output from this mal-function detector; a reference numeral 25 represents an engine operating condition detector which detects the operating conditions of the engine such as, for example, a throttle valve aperture detector (not shown in the drawing), an engine speed detector (not shown in the drawing), and so forth; a reference numeral 26 represents an intake air flow estimating circuit which estimates the quantity of the intake air based on the throttle valve aperture signal, the engine speed signal, and so forth from the engine operating condition detector 25, without directly measuring the intake air flow by the intake air flow measuring device 3; and a numeral 27 refers to a signal selector which functions to change over a signal Q.sub.0 which is directly forwarded from the intake air flow measuring device 3 and a signal Q.sub.1 which is forwarded from the intake air flow estimating circuit 26 by means of a judging signal a sent from the mal-function detecting device 23, this signal selector constituting an intake air flow estimating device 28 together with the intake air flow estimating circuit 26. A reference numeral 29 designates a mixing ratio control device for determining a mixing ratio of air and fuel by taking into consideration of the signal forwarded from the signal selector 27 together with an operating condition parameter C; and numeral 30 refers to a fuel feeding device which controls the fuel injection quantity based on an output from this mixing ratio controlling device 29, a control unit 31 being constructed with the mixing ratio control device 29.
In the following, explanations will be made as to the operations of the conventional fuel injection control device of the internal combustion engine as constructed in the above-mentioned manner. First of all, in the case of the intake air flow measuring device 3 operating regularly, the signal Q.sub.0 which corresponds to the air flow quantity as measured and which is forwarded from the intake air flow measuring device 3 is selected by the signal selector 27, and then is inputted into the mixing ratio control device 29. The mixing ratio control device 29 determines the mixing ratio by taking into consideration of the parameters for the operating conditions based on this signal Q.sub.0. On the basis of this mixing ratio, the fuel feeding device 30 controls the fuel injection quantity to thereby maintain a favorable state of combustion.
On the other hand, in the case of the intake air measuring device 3 being out of order, the mal-function detecting device 23 detects such abnormal operation, that is, disorder in the intake air flow measuring device 3, and outputs the judging signal a, which is imparted to the signal selector 27, on account of which the mixing ratio control device 29 takes into it the signal Q.sub.1 which corresponds to the estimated air flow quantity and which is forwarded from the intake air flow estimating circuit 26. Accordingly, the mixing ratio control device 29 determines the mixing ratio by taking into consideration of the parameters for the operating conditions on the basis of the above signal Q.sub.1. The operations thereafter are the same as those when the device is operating regularly.
Accordingly, the device as shown in FIG. 8 is able to continuously operate the internal combustion engine, even when the intake air flow measuring device 3 should become out of order, by actuation of the fuel feeding device 30 based on the estimated quantity of the air flow to be obtained from the detection signal of the engine operating condition detecting device 25.
On the other hand, however, no consideration whatsoever has been taken in this device shown in FIG. 8 as to the point of its improvement in the operativeness of the engine and the composition of the exhaust gas during the idle running of the engine.
However, the device as shown in FIG. 7 has a problem such that it can no longer continue the engine operation, when the air flow-meter 3 for detecting the intake air flow gets out of order, while the device as shown in FIG. 8 has its own point of problem such that improvement in the operativeness of the engine and the composition of the exhaust gas during the engine idling cannot be realized.
Both of these devices, though they are identical in the general concept of the fuel injection control device of the internal combustion engine, are completely different in their actual construction, hence it is difficult to consider these two devices taken together. Even if the failure-time control device as shown in FIG. 7, wherein the fuel injection is controlled by the intake air flow estimated on the basis of the throttle valve aperture signal and the engine speed signal, is applied to the fuel injection device as shown in FIG. 8, since the device of FIG. 7 is in such a construction that it once separates the intake air which has been introduced into it through the air inlet port 1 into the one passing through the throttle valve 5 and the other passing in and through the by-pass port 8 and the by-pass passage 6, and yet, in this by-pass passage 6, since the aperture (degree of opening) of the flow control valve 7 is adjusted to vary the quantity of the intake air flowing in and through it, the relationship between the aperture of the throttle valve 5 and the quantity of the air flowing in and through the intake manifold 10 cannot be determined primarily, even if the number of revolution of the engine is constant. In addition, the throttle valve 5 during the idle running of the engine is approximately in its full open state. As the consequence of this, with the device of FIG. 8, estimation of the intake air flow becomes difficult from the throttle valve aperture signal, hence it is not possible to find out the fuel quantity commensurate with the intake air flow, and, when a satisfactory combustion is controlled by the intake air flow as estimated on the basis of the engine speed (number of revolution), there takes place in some cases a large difference between the estimated air flow quantity and the actual air flow quantity; in particular, during the idle running of the engine, it is no longer possible to find the fuel quantity proportionate to the actual intake air flow, which results in raising such a problem that no favorable engine combustion can be effected.